The new gen of A/C electric compressors have moved the HOT heat producing electronics on top of the compressor. Now not only dose this system rely on a full refrigerant charge to return oil back to the compressor and cool the hot electric motor to keep it alive but the refrigerant needs to cool the power inverter for the compressor to. Today I was looking at my Prius C and also notice that the refrigerant sight glass level was vary low ( THIS IS NORMAL UNDER A LOW LOAD CONDITION ). No the A/C system is not low under certain conditions, but if a prius owner were to go into a shop and ask at a service to just inspect the A/C the mechanic would say its vary low, we need to top it off? WRONG!!!. Ya 20 years ago even if I seen this I would have said the system was low and the high side discharge line was cool to the touch, this is not right ( BUT IT IS RIGHT UNDER CERTAIN CONDITIONS ). The new A/C system of today do not follow many of the old rules of air conditioning. Under no circumstances should a shop tell you all we need to do is add refrigerant or tell you just because there is some bubbles in the sight glass you need a A/C service. Run the other way and never go back. If your Prius goes to a body shop or repair shop to have the condenser replaced or just removed for some other repair work insist they only use new ND-11 refrigerant oil and also ask to see their refrigerant recovery and recycle machine and look at the refrigerant moisture indicator. It should be green NOT YELLOW!!!. Ask to see that they have a refrigerant identifier if they do not, have some one who dose do your A/C service. Just because they have a sigh out side saying *** WE DO AIR CONDITIONING or A/C SERVICE HERE*** dose not mean they know nothing more then replacing part getting it right some times, or at least as long that when the compressor burns up you don't think it had any thing to do with the last shop who did the so called service or repair. PS... and some of the new Prius C electric compressors are a little more noisy under some working conditions also some times you will see vary little refrigerant flow with lots of air almost no movement when the compressor is on under some load conditions.